1. Field of the Invention
The present invention concerns a matrix-addressable optoelectronic apparatus comprising a functional medium in the form of an optoelectronically active material provided in a global layer in sandwich between first and second electrode means, each with parallel strip-like electrodes wherein the electrodes of the second electrode means are oriented at an angle to the electrodes of the first electrode means, wherein functional elements are formed in volumes of the active material defined at respective overlaps between the electrodes of the first electrode means and the electrodes of the second electrode means to provide a matrix-addressable array with the electrodes in contact with the active material, wherein a functional element in the active material can be activated by applying a voltage to the crossing electrodes defining the element to form a light-emitting, light-absorbing, reflecting or polarizing pixel in a display device, or alternatively by incident light to form a pixel in an optical detector and outputting a voltage or current via the electrodes crossing at the pixel, said active material in either case being selected as an inorganic or organic material and capable according to the intended function either to emit, absorb, reflect or polarize light upon being a activated by an applied voltage or to output a voltage or current when stimulated by incident light, or both, whereby the addressing of a pixel in any case takes place in a matrix-addressing scheme, and wherein the electrodes of at least one of the electrode sets are made of a transparent or translucent material.
The present invention also concerns an electrodes means for use in the matrix-addressable optoelectronic apparatus, comprising a thin-film electrode layer with electrodes in the form of parallel strip-like electrical conductors, wherein the electrode layer is provided on an insulating surface of a backplane.
The present invention particularly concerns apparatuses and devices comprising functional elements in a planar array, wherein the functional elements are addressed via respectively a first electrode means with parallel strip-like electrodes arranged in contact with the functional elements on one side thereof and another electrode means with similar electrodes, but oriented perpendicular to the electrodes of the first means and provided in contact with the opposite side of the functional element. This constitutes what is called a matrix-addressable device. Such matrix-addressable devices can comprise e.g. functional elements in the form of logic cells, memory cells or in case of the present invention, pixels in a display or photodetector. The functional elements may include one or more active switching means, in which case the matrix-addressable device is termed an active matrix-addressable device, or the functional elements may consist of passive means only, e.g. resistive or capacitive means, in which case the matrix-addressable device is termed a passive matrix-addressable device.
The latter is regarded as providing a most efficient way of addressing, for instance in case of memory devices, as no switching elements, viz. transistors are required in memory cell. It is then desirable to achieve as high storage density as possible, but present design rules which set a lower limit to the cell are, also limit the fill factor thereof, i.e. the area of the active material of the matrix-addressable apparatus that actually can be used for the functional elements thereof.
2. State of the Art
A prior art passive matrix-addressable optoelectronic apparatus is shown in FIG. 1a and comprises an essentially planar global layer of optoelectronically active material 3 in sandwich between a first electrode means EM1 comprising parallel strip-like electrodes 1 of width w and spaced apart by a distance d and a similar second electrode means EM2 comprising parallel strip-like electrodes 2 of the same width w, but with the electrodes 2 arranged perpendicular to the electrodes 1 of the first electrode means EM1. In the global layer of active material 3 the overlap between the electrodes 1, 2 of the respective electrode means defines a pixel 5 in the active material 3. By applying voltage to the electrodes 1,2 crossing at this location, the pixel 5 will for instance emit light when the apparatus is configured as a display and by applying incident light to the pixel 5, a detectable current will be output on the electrodes 1,2 when the apparatus is configured as a photodetector.
FIG. 1b shows the prior art device of FIG. 1a in a section taken along the line Xxe2x80x94X making the layout of the electrodes 1,2 and the global layer of the sandwiched active material 3 as well as the location of the pixels 5 apparent. The active material 3 of the global layer usually has properties such that an application of the voltage to crossing electrodes 1,2 only will affect the pixel 5 at the crossing thereof and not neighbouring pixels or cells at the electrodes crossings in the vicinity of the former. This can be achieved by providing the active material with anisotropic conducting property, such that electrical conduction only can take place in a perpendicular direction to the surface of the active material and between the overlapping electrodes, with no current flowing through the global layer to the other pixels. The size and density of pixels 5 will depend on a process-constrained minimum feature that can be obtained in the manufacturing process. Such features are, e.g. when electrodes are laid down as metallization which afterwards is patterned in a photomicrolithographic process resorting to photolithographic masks and e.g. etching, dependent on the process-constrained smallest feature f that can be defined by the mask and its value will in its turn depend on the wavelength of the light used. In other words, this feature f will usually within the scope of today""s technology be limited to say 0.15-0.2 xcexcm, and hence the width w of the electrodes 1,2 and the spacings therebetween will be of about this magnitude.
In that connection it should be noted that the value 2 f usually is termed the pitch and that the maximum number of lines per unit length as obtainable with prior art fabrication technology is given by the factor 1 f and correspondingly the maximum number of features per unit area by the factor 1 f2. Hence if the area 4 shown in FIG. 1 is considered, it will be evident that the size of a pixel 5 is given by f2 as apparent from FIG. 1c which shows the area 4 in greater detail. Each pixel 5 requires a real estate corresponding to the area 4, the size of which is 4 f2, in other words, four times larger than the area f2 of the pixel. This consideration shows that the matrix in FIG. 1a has a fill factor of 0.25, i.e. f2/4 f2. The degree of exploitation of the area offered by the layer 3 is thus low. In order to arrive at a higher fill factor or a higher density of pixels 5 in the global layer it would be desirable to increase either the fill factor or to obtain a higher resolution in the process-constrained features of the matrix, e.g. into the sub-0.1 xcexcm range. However, although this may increase the total number of pixels in a similar area, still it would not be able to guarantee a higher fill factor.
In view of the above considerations it is a major object of the present invention to enable an increase of the fill factor in a matrix-addressable optoelectronic apparatus of the afore-mentioned kind to a value approaching unity and to achieve a maximum exploitation of the real estate offered by the global layer of the active material 3 in such apparatuses without actually being constrained by the actual or practical size of the process-constrained minimum feature f, as the fill factor will not be influenced by decrease in f, although such a decrease of course, will serve to further increase the maximum number of pixels obtainable in a global layer of the active material 3.
The above objects as well as further advantages and features are achieved according to the present invention with a matrix-addressable optoelectronic apparatus which is characterized in that the electrodes of each electrode means are provided in a respective electrode layer, that the electrodes in the electrode means all have about the same width w, that electrodes of each electrode means are mutually insulated electrically by an insulating thin film of thickness xcex4, the magnitude of xcex4 being a fraction of the width w, and that minimum magnitude of w is comparable to a process-constrained minimum feature size f, whereby the fill factor of the pixels in the optoelectronically active material relative thereto is close to 1 and the number of pixels approaches a maximum defined by the total area A of the active material sandwiched between the electrode means, and said feature size f, said maximum thus being defined by A/f2.
In an advantageous embodiment of the apparatus according to the invention, the optoelectronically active material is an anisotropic conducting organic material with diode domains contacting the electrodes of the electrode means, and then the organic conducting material can preferably be a conjugated light-emitting and/or photoelectric polymer, whereby the matrix-addressable apparatus can be operated as a display or as a photodetector or both.
In this advantageous embodiment of the apparatus according to the invention, the diode domains can be capable of emitting light when stimulated by an applied voltage, whereby the matrix-addressable apparatus can be operated as a display, or the diode domains can be capable of outputting a current or voltage when stimulated by incident light, whereby the matrix-addressable apparatus can be operated as s photodetector.
The above objects as well as further advantages and features are also achieved according to the present invention with an electrode means which is characterized in that the thin-film electrode layer comprises
a first set of said strip-like electrodes of width wa and thickness ha provided on the backplane, the electrodes of the first set being mutually spaced apart by distance d equal to or greater than wa, a second set of said strip-like electrodes with width wb and thickness hb provided in the spacings between the electrodes of the first set and electrically insulated therefrom by a thin film of an electrically insulating material with thickness xcex4 and at least extending along the side edges of the parallel electrodes and forming an insulating wall of thickness xcex4 therebetween, the magnitude of xcex4 being small compared to the magnitude of either wa or wb, with the spacing distance d between the electrodes of the first set being wb+2xcex4, and that the electrode layer with electrodes and the insulating thin film forms a global planar layer in the electrode means on the backplane thereof.
In an advantageous embodiment of the electrode means according to the present invention the insulating walls between the electrodes of the first set and the electrodes of the second set form portions of the thin film of insulating material provided in a layer covering the side edges of the electrodes of the first set up to the top surface thereof as well as the backplane in the spacings between the former, and that the electrodes of the second set are provided in recesses between the wall portions of the insulating thin film and above a portion thereof covering the backplane, the electrodes of the second set being flush with the top edge of the insulating walls as well as the top surface of the electrodes of the first set, whereby the electrodes of the second set have the height hb=haxe2x88x92xcex4, and that the electrode layer with electrodes and insulating material form a global planar layer of thickness ha in the electrode means on the backplane thereof.
In at least one of the electrode means according to the invention the electrodes as well as the backplane must be made of a transparent or a translucent material, when the electrode means are used in the inventive apparatus. The invention shall now be explained in more detail with reference to exemplary embodiments in conjunction with the appended drawing figures,